In the manufacture of a semiconductor element bonding substrate or a semiconductor device, when connecting metal materials, or when connecting electronic parts such as semiconductor elements to a printed circuit board, typically soldering is used. The solder material that is used in soldering is formed into various shapes such as a wire, ribbon, sheet, pre-formed material (punching material), ball, fine powder and the like.
The solder material is such that oxidation occurs easily in the presence of oxygen, and an oxide film is formed on the surface during storage. Particularly, in the case where the solder material will be used after a long time has elapsed since the manufacturing of the material, oxidation proceeds and the oxidation film becomes thick, which invites bonding defects such as a decrease in the wetting extendability and bondability, or the occurrence of empty gaps (voids). In addition, the solder material is melted under high temperature during use, so the oxide film becomes even thicker. When thick oxide film that is formed in this way exists between objects that are to be bonded after bonding, problems occur in that there is bad conductivity and a decrease in bondability.
To handle these problems, conventionally, typically flux was applied beforehand to the surface of the solder material, or flux was used during bonding. As this kind of flux an inorganic acid, an organic acid, or a resin having a rosin base are known. However, an inorganic acid flux has strong activity as a flux, which may cause a decrease in the electrical properties, or cause corrosion of the bonded materials. Moreover, organic acid flux has a disadvantage in that the strength of the reaction with oxide film is weak. Furthermore, resin flux is such that flux residue is generated, and so from the aspect of electric reliability, it becomes necessary to clean and remove that residue using a solvent such as a fluorocarbon. In this way, there are problems when using any flux for uses such as a semiconductor device, which obstructs the reduction of cost.
As a way for preventing the oxidation of solder material using something other than flux, a method of forming a coating film on the surface of the solder material has been proposed. For example, JPH10166177 (A) proposes a method of coating the surface of solder material using a material that includes phosphorous and that is composed of a phosphorous compound and a surfactant, and more specifically a phosphate compound that includes a fluoroalkyl group and a nonionic surfactant. Moreover, JP2001105172 (A) and JP2001144111 (A) propose a method of coating the surface of a solder material with a nonionic surfactant, and more specifically, polyoxyethylene sorbitan aliphatic acid ester. However, all of these methods form a coating by a wet method, and it is difficult to form a thin coating film that has an even thickness everywhere of 200 nm or less. Therefore, with the coating films formed using these methods, there is large fluctuation in the film thickness, and it is not possible to sufficiently suppress oxidation of the solder material. There is also a possibility that due to the existence of this coating film, problems such as a decrease in the wetting expandability and the bondability of the solder material, and the occurrence of gaps (voids).
In regard to this, JP2010058111 (A) relates to the formation of a reflective surface of a reflector in a vehicle lamp, and discloses a dry type of surface processing that uses a reduced pressure plasma CVD method to layer an undercoat layer, a reflective layer using an evaporated silver film or the like, and a topcoat layer on a base material. In this method, a silicon oxide film (SiOx film) that is formed by plasma polymerization of a silane compound onto an undercoat layer and topcoat layer is used. With this kind of dry surface processing, it is possible that a comparatively thin coating film could be formed evenly everywhere over the entire object. Moreover, this method differs from a wet method in that the film forming material is not spread inside the factory, so it is possible to maintain a good working environment. However, in surface processing using a reduced pressure plasma CVD method, generally large and expensive vacuum equipment or pressure reducing equipment is necessary, which brings about an increase in the production cost and worsening of productivity.
On the other hand, JP2004510571 (A) and JP2009286041 (A) disclose surface processing that uses an atmospheric pressure plasma CVD method. More specifically, JP2004510571 (A) discloses a method of forming a coating (coating film) that includes polydimethylsiloxane and the like on the surface of a substrate by introducing a liquid-spray type coating forming material that includes an organic silicon compound into an atmospheric pressure plasma arc, and exposing a substrate, which is metal or the like, with the spray type coating forming material. Moreover, JP2009286041 (A) discloses technology of manufacturing a colorless gas-barrier film by performing surface processing using an atmospheric pressure plasma CVD method that uses a specific hydrocarbon such as n-pentane, n-hexane and the like on the surface of a metal oxide film that is formed on the surface of a resin film. The atmospheric pressure plasma CVD method disclosed in these documents differ from a reduced pressure plasma CVD method in that vacuum equipment or pressure reducing equipment are not necessary, so problems with increased production cost or worsening productivity do not occur.
However, in the technology disclosed in the literature above, plasmatization of a reaction gas, and activation of atomized spray type coating forming material is simultaneously performed, so activation of the spray type coating forming material becomes irregular, and it is difficult to form a minute coating film everywhere over the entire substrate surface. Moreover, the technology in the literature above is not intended for preventing oxidation of the surface of a solder material, and does not take into consideration problems such as the behavior of the coating film during melting of the solder material, the effect on the wetting extendability and bondability due to the existence of the coating film, the occurrence of gaps and the like.